I recently lost one of my hard drives and have to reinstall windows 7. I'd rather not go back and install windows xp or vista and upgrade, and I know there are tricks do doing a clean install with an upgrade key, but none of them have worked for me. I tried the double install trick, which gave me the "key is not valid" message. Then I tried the regedit and rearm, which didn't work either. It was weird because my 'MediaBootInstall' key was already set at '0' instead of '1', but the activation still gives me the "key is not valid" message.